Cost of a pinion bearing replacement? Or a Differential Rebuild?

My truck is giving a periodic thrum sound from somewhere in back. About a half second pulse every 2 or 3 seconds. Cyclic period of the pulses does not change with speed, but the pitch of the thrum does slightly increase.

This symptom sounded just like my two front failed wheel bearings so thinking one of the rear wheel bearings was going, I replaced both of them.

This did not fix the problem.

So I'm thinking maybe the problem is in the differential? Or the drive shaft?

I did not service my diff fluid until 100k. Fluid was pretty dark and there was a single splinter of metal on the magnet when I cleaned it.

Now I'm at 125k and the noise problem started showing. At 125k the fluid was clean almost like new when I removed it. Only light haze of dark on the magnet when I cleaned it the second time.

1: Are these the sounds typical of a failed bearing in the differential or a failing U joint on the shaft?

2: Secondly, if I need to have something in the differential replaced, say the pinion bearings, what can I expect in terms of labor charge from a mechanic?

Rock Auto sells differential rebuild kits. This one uses Timken bearings and clocks in at about $500. So I imagine that would be a lower bound on parts if a mechanic does a rebuild. I've noticed that mechanics like to inflate their parts quite a bit.

Watching some videos, the job doesn't look like it's that difficult to me, but it does require some special tools. Still, there are a couple steps that seem like they demand experience (adjusting for play in the bearings, getting the retainers installed without damaging threads).

3. So third question: are most shops likely competent with differentials or should I seek out a mechanic that specializes in them? How would I find such a guy?

(Central Ohio)

These problems are killing me financially. I welcome your advice.

Thanks for your attention.

 

I’d buy a complete 3rd member.
It’s drop in. It doesn’t get any easier.
There’s not much skilled required.

https://eastcoastgearsupply.com/c-1065072-assembled-3rds-clamshells-05-15-tacoma.html

 

Wow, that’s much more affordable than I imagined. And DIY.

I’ll be sure to vote for you for Tip of the Year award when that event comes up on TacomaWorld.

Thx.